This invention relates to a device for measuring magnetization characteristics of a magnetic thin film attached to magnetic tapes, magnetic stripes on magnetic cards, magnetic discs or the like.
Along with the progress in the information society, magnetic recording media such as magnetic cards, magnetic tapes or magnetic discs have formed a considerably large market which is expected to further expand in the future. In order to stably manufacture these media in a large quantity at a low cost and improve product quality, further research and developing efforts are required. A measurement device for measuring magnetization characteristics of these media is one of the supporting means for such efforts. For example, a DC magnetization characteristic automatic recording system (Model 3257, Yokogawa Electric Corporation in Japan) and DC magnetized B-H characteristics automatic recording systems (Model BHS-40, BHH-50 and BHU-60, Riken Denshin Kabushiki Kaisha in Japan) are currently commercial available for recording the magnetization characteristics of magnetic films, such as the magnetic film on a magnetic tape.
As an example of detection by those systems, a detection method popularly used for magnetization characteristics on an annular sample will be described. When a magnetic material or an object of detection is charged with a magnetic field H, the density of the magnetic flux .PHI. generated on the material changes according to the intensity of the magnetic field H. When the magnetic field H is plotted on a horizontal axis, and the magnetic flux .PHI. on a vertical axis, a magnetization curve or a hysteresis loop is obtained. More specifically, as shown in FIG. 1, an anuular magnetic material 100 is wound with a magnetizing coil 101 (the number of windings designated N.sub.1) on the primary side thereof and with a detection coil 102 (the number of windings designated N.sub.2) on the secondary side thereof. The magnetization coil 101 is supplied with sine wave signal of a low frequency from a low frequency oscillator 103, and a resistance R.sub.1 is inserted in series as shown.
Since the magnetic field H in the magnetic material 100 can be regarded as proportional to the electric current I.sub.1 passing through the magnetizing coil 101, if the length of the magnetic path of the magnetic material 100 is denoted as l, the following relation holds: ##EQU1## The generated magnetic flux .PHI. is obtained by integrating the output voltage V.sub.2 of the detection coil 102. Namely, since the output voltage V.sub.c can be determined by equation (2) below. ##EQU2## The following relation therefore holds as shown below as equation (3). ##EQU3## A magnetization curve (.PHI.-H curve) can be obtained by measuring the voltages V.sub.1 and V.sub.c. If the voltage V.sub.2 is plotted on the vertical axis, the output proportional to magnetic permeability is obtained.
The magnetic material measurement system based on the above described principle is disclosed in "Yokogawa Giho" Vol.17, No. 2, pp. 49-72, 1973. Although the measurement system is intended for universal use, as it is applicable to the measurement of having a materials of high permeability such as plates or blocks of permanent magnets, magnetic powder, magnetic thin film, etc., the measurement system is still not entirely free of problems in performance, operability and price. Moreover, when used for measuring magnetic stripes prepared by thermal transfer or application on a paper card, a card or a passbook on which magnetic tapes are pasted, or a magnetic card coated on its surface in magnetization characteristics, a sample 110 of the magnetic thin films should be cut out from the card or book as shown in FIG. 2, adjusted in size to accommodate the size of the system, and sorted in a layer of about ten cards before being subjected to the actual measurement. The system therefore is extremely cumbersome. The measurement system, moreover, is incapable of measuring the magnetization characteristics of magnetic stripes on a magnetic card as incorporated on the card. It was heretofore extremely difficult to measure the absolute value of the magnetization characteristics of a magnetic stripe medium, a magnetic disc medium or the like.
Moreover, users have to visually read, calculate and judge the magnetization characteristics such as saturated flux, residual magnetism and coercive force from a hysteresis curve drawn as a hard copy by an X-Y recorder mounted on the system in order to determine the acceptance of the magnetization characteristics. The work therefore was considerably combersome. No measuring device has so far achieved an effective analysis of process capability of the magnetization characteristics. The currently available systems are inconveniently bulky in size as a whole since discrete components such as an exciter/amplifier, a signal processing integrator, an X-Y recorder, etc. are merely combined.